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The sperm whale (Physeter macrocephalus) is the largest species of toothed whale, with adult bulls (males) growing to be about 15–18 metres (49–59 ft) long, and weighing about 45–70 metric tons (44–69 long tons; 50–77 short tons). The two kogiid species are much smaller, at only around 2.5 to 3.5 metres (8 ft 2 in to 11 ft 6 in) in length, and weighing 350–500 kilograms (770–1,100 lb).

The bodies of physeteroids are robustly proportioned, with paddle-shaped flippers. The lower jaw is always relatively small and thin relative to the upper jaw. The nasal bones of these whales are distinctly asymmetrical, with the blowhole being located on the left side of the head; in the sperm whale this is near the top of the head, while on the kogiids it is further forward. All species have a large number of similar, and relatively simple, teeth. In the kogiids, and sometimes also in the sperm whale, the teeth in the upper jaw do not erupt, and are sometimes altogether absent.[1]

The eyes of physeteroids are unable to swivel in their sockets, and possess only a vestigial anterior chamber. It is likely that echolocation is a far more important sense to these animals than vision.[1]

Another common characteristic is the spermaceti, a semi-liquid waxy white substance filling the 'case' or spermaceti organ in the whale's head, which is thought to be involved in providing ballast for diving and maintaining buoyancy. This may be done by flushing cold water through the nose, hardening the spermaceti, to dive, and pumping warm blood to melt the spermaceti to surface. All three species dive to great depths to find food, although the sperm whale is believed to dive much deeper than either of the kogiids. Members of both families eat squid, fish, and even sharks.

Gestation lasts from nine to fifteen months, depending on species. The single calf remains with the mother for at least two years, before being weaned. Physeteroids do not reach full sexual maturity for several years. All species congregate in 'pods' or herds, consisting of mostly females, calfs, and adolescent males, although these pod sizes are typically smaller in the kogiids.[1]

The earliest sperm whale fossils are known from the late Oligocene – about 25 million years ago,[2][3] with an ancestry tracing back from the latest Eocene before diverging from the remainder of the Odontocetid line, leading to the dolphins, and porpoises.

The close relationship between extant Physeteridae and Kogiidae is confirmed in recent molecular studies using mitochondrial cytochrome b,;[5][6] on the basis of these analyses, their nearest relatives appear to be the Ziphiidae on one hand, and the Mysticeti and Platanistidae on the other. The last cited paper also favours the grouping of Physeteridae and Kogiidae in a single superfamily, Physeteroidea, as has sometimes previously been suggested. Bianucci & Landini, 2006[7] suggest that Diaphorocetus, Zygophyseter, Naganocetus and Aulophyseter pre-date the inferred split of Kogiidae and Physeteridae and thus would restrict the family Physeteridae to those genera that post-date this split (a cladistic view).

Members of the suborderOdontoceti, the suborder containing all the toothed whales and dolphins. One extant species of the genus Physeter, which is placed in the family Physeteridae. Two species of the related extant genus Kogia, the pygmy sperm whaleKogia breviceps and the dwarf sperm whaleK. simus, are sometimes also placed in this family, or else are placed in their own family, Kogiidae.[8]

The following is a summary of the classification of extant and extinct (†) taxa: